Certain conventional systems use a "transactional" model for exchanging information between nodes of a data processing system. In a conventional transactional model, two applications initiate a synchronous "transaction" that is maintained for as long as information is being exchanged between the nodes. The transactional model requires that a transaction be defined for each business activity. When nodes on widely disparate portions of a network attempt to communicate via the transaction model, it is often difficult to define a transaction that works well on all parts of the system. Moreover, a transaction can only involve the nodes that began the transaction. Another node cannot join the transaction in the middle. This scheme is unsuited for a system in which nodes do not know about all other nodes in the system.
Many commercial enterprises still use software that was developed long ago and is no longer supported by its manufacturer. Such software is called "legacy software." It is not always possible or desirable to modify existing legacy software to operate with a new networked system. The legacy software may be very complex, making it difficult and expensive to modify. A company may be wary of making modifications to a stable system that is working consistently. Moreover, there may not be any computer programmers at a company who understand the legacy system in enough detail that they can make modifications to it. Lastly, a company may not have the source code for a legacy application if it purchased the application from a commercial vendor. What is needed is a way to integrate legacy software into a networked system.